This invention relates generally to a matrix type multi-color display device and to a method of producing color filters in a matrix type multi-color display device using thin film transistors (TFT) and color filters.
A matrix type multi-color display device using TFTs, as shown in FIG. 1, has been proposed conventionally. In this device, thin film transistors 1 are arranged in a matrix in such a manner that their gate electrodes 7 are connected in rows to row drivers R.sub.1 -R.sub.n while their source electrodes 12 are connected in columns to column drivers C.sub.1 -C.sub.n, and color filters 2 of different colors are provided over the display electrodes 13 connected to drain electrodes 14 of the transistors. Some display material 3 which operates as an optical shutter when a voltage is applied thereto, such as a liquid crystal or an electrochromic material, is interposed between each display electrode 13 and counter electrode 5 connected to the ground, and a capacitor 4 is connected between each display electrode 13 and either ground or the gate electrode connected to the row driver of the preceding stage. There is a delay between the application of an electric signal across the display material and the change in optical characteristics at that point, so the capacitors 4 are provided to extend the time in which the signal voltage is held across the display material to at least its relaxation time, and thus let the display material respond to the signal. Each transistor 1 provides a threshold value therefor.
FIG. 2 shows a section through the matrix type multi-color display device of the construction described above. First, two substrates 6 and 11 are prepared. One of the substrates 6 has a transparent counter electrode 5 over its entire surface and the other 11 is provided with a plurality of gate electrodes 7 made of Cr of Al, a gate electrode pad 8 connected to each gate electrode 7, an insulation layer 9 of SiO or Al.sub.2 O.sub.3 over the pads 8, and a semiconductor layer 10 of CdSe or CdS. Source lines 12 of Al are formed on top of the semiconductor layer 10 in the direction at right angles to the gate electrodes 7, and a display element cell is formed at each interection of the column and row lines. A display electrode 13 for each display element cell consists of a transparent conductive layer and is connected to a drain electrode 14. The display electrode 13 not only serves as a display electrode but also forms one electrode of a capacitor 4 together with the gate electrode pad 8 of the adjacent transistor. A color filter layer 2 is formed on each display electrode 13, and display material 3 fills the space between the substrate 6 and the substrate 11. In the matrix type multi-color display device of this kind, a voltage is applied between specific row and column lines to turn on a selected transistor so that a voltage is applied across the display material, the optical shutter is operated, and the color of the selected color filter is displayed. Thus, a multi-color display device which can be matrix-driven can be obtained by changing the colors of the color filters of each display element cell.
A multi-color display using color filters is extremely effective because the method is easy and simple to practice, any colors can be obtained, and various display materials and systems can be combined.
When manufacturing this multi-color display device using color filters, however, the pattern of display electrodes and the pattern of color filters formed on the surface of the display electrodes must be arranged so that there is no discrepancy between them. Particularly when making a color graphic display using a fine pattern of the three primary colors, there is the serious problem that it is very difficult to form the display electrodes and color filters without any discrepancy between them. Changing colors to reaize a multi-color display is another problem which makes the production process complicated. Particularly when the coloring is effected by the use of dyes, resist printing steps must be included to prevent the portions that have already been dyed from being dyed again in subsequent dyeing steps, making the production process all the more complicated. In addition, the resist printing technique itself presents difficult problems which must be solved independently.
To produce the color filters, methods using screen printing, photolithography and the like are generally used. Resist printing is not necessary when using screen printing but there is a limit to the miniaturization of the pattern that can be produced, so that the greater the number of the colors in the display, the lower the accuracy of the print position and thus the greater the discrepancy from the display pattern. Photolithography can provide a fine pattern, but a photolithographic step is necessary for each change of color and resist printing must be provided between dye steps, to prevent double dyeing. Thus, the production process become complicated, and the advantage of a simple means of realizing a multi-color display can no longer be obtained.